Method of producing alloys of alkali metal and lead having a grain form and structure suited to lead alkyl synthesis



s. c. PYK 2,561,636 ING ALLOYS OF ALKALI METAL GRAIN FORM AND STRUCTURESUITED TO LEAD ALKYL. SYNTHESIS Filed July 9, 1947 July 24, 1951 METHODOF PRODUC AND LEAD HAVING A A. I V H H H a 2 hh A ,1 m 7 mm PatentedJuly 24', 1951 METHOD OF PRODUCING ALLOYS F AL- KALI METAL AND LEADHAVING A GRAIN FORM AND STRUCTURE SUITED T0 LEAD ALKYL SYNTHESIS SvenChristian Pyk, Nynashamn, Sweden, assignor, by mesne assignments, to TheAssociated Ethyl Company Limited, London, England Application July 9,1947, Serial No. 759,866

In Sweden April 22, 1943 Section 1, Public Law 690, August 8, 1946Patent expires April 22, 1963 2 Claims. 1

During reactions in heterogeneous systems in which a participating,solid reaction component is simultaneously dissolved, the reactionprocess is often greatly influenced both by the surface area (particlesize) and the body structure of said component. It is thus as a rule ofgreat importance for the reaction velocity and the uniformity of suchprocesses in which a metal (by which, in the following, also metalalloys are to be understood) takes part, that the metal has not only auniform grain size but also a suitable crystal size and crystalarrangement. This is for instance an important condition in thepreparation of tetraethyl lead and other lead alkyls from an alloy Ofsodium and lead.

This alloy generally consists of lead and sodium in amounts proportionalto their atomic weights. It is also possible to partly replace sodium bypotassium, whereby a better yield is obtained in the synthesis. Thisalloy composition corresponds to a real chemical compound of lead andalkali metal, having the formula MePb, wherein Me represents an alkalimetal selected from a class consisting of sodium and potassium. Thesodium alloy has the composition NaPb, containing per cent by weight ofsodium.

The reaction in the lead alkyl synthesis for the preparation of e. g.tetraethyl lead proceeds substantially according to the formula:

Since this reaction takes place between solid alloy and liquid orgaseous ethyl chloride, i. e. in a heterogenous system, the form of thealloy will greatly influence the reaction velocity. It has previouslybeen found that dustfree grains of equal size of this alloy areespecially suited for carrying-out the highly exothermic synthesis.Grains of the size of 3-5 mm. are considered to be especially suitable.This product has hitherto been obtained by crushing the solidifiedalloy, which is very brittle, or by vigorously stirring the molten alloywith a simultaneous freezingout or by a combination of these methods inchilled mills or crushers. This will result in a comminuted product ofpieces or grains from which dust and minor particles must first beremoved by sifting, since it has been found that these minor grainscause irregularities in the reaction process in question, which arediflicult to control.

It has now been found, however, that properties favourable in saidrespects can be obtained by allowing the alloy, after melting, to hardenon a cooled roller of particular shape which is partly immersed into thealloy bath or in some other suitable manner is kept in direct contactwith it, whereby the alloy is suuplied to the surface of the roller and,after hardening, continually scraped off from it during the rotation ofthe roller.

According to the present invention the adhesion of the molten alloy tothe roller is facilitated and the size of the separated alloy flakeslimited by providing the roller surface with grooves and ridges orsimilar elevations. If the grooves etc. are placed mutually equidistantand arranged at right angles to the axis of rotation of the roller,weakenings are 'produced in the solidifying alloy layer, whichweakenings cause said layer, when being scraped off, to loosen intostrips of equal width which, in turn, on account of the brittleness ofthe alloy and the crystal growth at right angles to the surface of thelayer, are automatically broken up at the grain boundaries into piecesof an even size.

The adhesion of the alloy to the roller can also be improved by coatingthe. surface of the roller with a metal or alloy of lower melting-pointthan the alloy separated on the roller by. cooling. Tin

or lead has thus proved to be especially suitable as a coating on theroller surface for the present purpose.

The device may be made closed, so that the process can be conducted inan atmosphere of neutral character. In this case the device is providedwith suitable gas-tight feeding and discharging arrangements.

By producing the alloy grains according to the methods of the presentinvention, due regard is taken not only to the above mentioned knownfact that an equal grain-size is favourable, but also to the fact thatboth the crystal size and the crystal arrangement have an essentialinfluence on the reaction process. Another advantage is that a productcooled down close to the temperature of the cooling medium is directlyobtained, whereby a further cooling of the easily oxidized alloy is notneeded, contrary to previously mentioned known methods, where such anextra measure has proven necessary.

0n the accompanying drawing is schematically shown an example of asuitable arrangement for carrying out the invention.

Fig. I is a vertical section through the apparatus and Fig. II a sectionat right angles to Fig. I. Figures III-V show details of suitable formsof the roller surface on a larger scale.

The rnolten alloy is introduced through pipe I and forms a bath 2 at thebottom of the appararoller by the outlet 5. When the roller rotates,

the molten alloy solidifies on the outside of the roller while fillingout the grooves and at the same time forming an integral layer over theridges. when the alloy layer, which is thus kept under a constantcooling, reaches the scraper 6 the alloy layer is detached from theroller and is simultaneously automatically broken up into fragmentswhich drop down through the spout I. It will be noted from Fig. thelayer of alloy is bent by the scraper through a rather sharp angle as itleaves the collecting drum and this causes it to break up since it isvery brittle.

In order to protect the alloy from atmospheric influence, the roller isenclosed in a gas-tight chamber 8 and supported in gas-tight bearings 9and In. The chamber is kept filled with a gas which is inert to thealloy. The rotation of the roller is effected by the driven shaft II.The spout I is provided with a suitable sluicing device to enable thealloy fragments to be removed from the chamber without admittance of theouter atmosphere.

Figs. III, IV and V show on an enlarged scale various modifications ofthe roller surface which have been found suitable. From these figuresthe various forms which the solidified metal layer'assumes will bereadily apparent. The form with square grooves shown in Fig. III hasproven particularly useful for effecting the desired di- 40 viding ofthe lead-sodium alloy into uniform fragments according to the invention.

II of the drawing that I claim:

1. In the process of forming small particles of lead-alkali metal alloyof uniform size and having crystals of relatively high purity and a sizewhich makes the particles particularly suitable for use in thepreparation of lead alkyls,

the steps which comprise forming a molten bath of a lead-alkali metalalloy having a composition corresponding substantially to the formulaMePb, wherein Me represents an alkali metal selected from a groupconsisting of sodium and potassium, which when in the solid state isvery brittle and which when solidified on surface forms a crystal growthperpendicular to the surface, passing through said bath a cylindricalsurface cooled below the solidification point of said alloy, saidsurface being provided with equally spaced parallel peripheral ridgeswith intermediate depressions, whereby a solidified brittle layer ofmetal with a crystal growth at right angles to the cooled surface isformed on said surface, scraping said solidified metal layer from saidsurface and bending it simultaneously through a sharp angle, whereby itis simultaneously and automatically broken along the depressions andcrystal boundaries into particles of substantially uniform size.

2. The process of claim 1 wherein the steps are performed in an inertatmosphere.

SVEN CHRISTIAN PYK.

REFERENCES CITED The following references are-of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,025,848 Wagner May '7, 19121,879,336 Foley et a1. Sept. 27, 1932 2,008,626 Murakami July 16, 19352,074,812 Sendzimir Mar. 23,193!

a cooled

1. IN THE PROCESS OF FORMING SMALL PARTICLES OF LEAD-ALKALI METAL ALLOYOF UNIFORM SIZE AND HAVING CRYSTALS OF RELATIVELY HIGH PURITY AND A SIZEWHICH MAKES THE PARTICLES PARTICULARLY SUITABLE FOR USE IN THEPREPARATION OF LEAD ALKYLS, THE STEPS WHICH COMPRISES FORMING A MOLTENBATH OF A LEAD-ALKALI METAL ALLOY HAVING A COMPOSITION CORRESPONDINGSUBSTANTIALLY TO THE FORMULA MEPB, WHEREIN ME REPRESENTS AN ALKALI METALSELECTED FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM, WHICH WHENIN THE SOLID STATE IS VERY BRITTLE AND WHICH WHEN SOLIDIFIED ON A COOLEDSURFACE FORMS A CRYSTAL GROWTH PREPENDICULAR TO THE SURFACE, PASSINGTHROUGH SAID BATH A CYLINOF SAID ALLOY, SAID SURFACE BEING PROVIDED WITHOF SAID ALLOY, SAID SURFACE BEING PROVIDED WITH EQUALY SPACED PARALLELPERIPHERAL RIDGES WITH INTERMEDIATE DEPRESSIONS, WHEREBY A SOLIFIFIEDBRITTLE LAYER OF METAL WITH A CRYSTAL GROWTH AT RIGHT ANDLES TO THECOOLED SURFACE IS FORMED ON SAID SURFACE, SCRAPING SAID SOLIDIFIED METALLAYER FROM SAID SURFACE AND BENDING IS SIMULTANEOUSLY THROUGH A SHARPANGLE, WHEREBY IT IS SMULTANEOUSLY AND AUTOMATICALLY BROKEN ALONG THEDEPRESSIONS AND CRYSTAL BOUNDARIES INTO PARTICLES OF SUBSTANTIALLYUNIFORM SOZE.